Field of Application
The present invention relates to a relay apparatus having a plurality of relays having respective contact switches, and to a relay system which incorporates such a relay apparatus.
Description of Related Art
Types of solenoid-operated relay apparatus have been proposed, having a plurality of solenoids with respective plungers for actuating respective contact switches, designed to be manufactured at lower cost than has hitherto been possible. The term “contact switch” is used herein to signify an on/off switch having fixed and movable contacts, which is actuated (switched between a non-conducting and a conducting state) by displacing the movable contact, as opposed to a semiconductor switching element such as a transistor. Examples of a solenoid-operated relay apparatus are described in Japanese patent publication No. 2013-211514, referred to in the following as reference 1. The relay apparatus of a first embodiment of reference 1 consists of a pair of solenoid-operated relays having respective contact switches, with only the solenoid of a first one of the relays having a corresponding electromagnetic coil, and with a magnetic flux generated by that electromagnetic coil being used to also activate the solenoid of the second relay. With the relay apparatus of reference 1, activation of the relays is performed in a specific sequence. Firstly, both of the relays are inactivated. The first relay is then activated by passing a sufficient level of current through the corresponding electromagnetic coil, pulling the corresponding plunger into a central aperture of the coil by magnetic attraction. Part of the magnetic flux produced by the electromagnetic coil of the first relay acts on the plunger of the second relay, but is insufficient to activate the second relay until the plunger of the first relay has become fully drawn into the central aperture of the electromagnetic coil. Both the relays are then left activated (both of the corresponding contact switches held in a conducting state).
Normally, leaving a pair of solenoids in an activated condition for a long period of time will result in a high level of electric power consumption. The apparatus of reference 1 is claimed to enable a reduction of 50% of the electric power required for maintaining both of the relays activated, by comparison with a conventional type of relay apparatus in which both of the relays are provided with respective electromagnetic coils.
However with the invention of reference 1, it is not possible to decrease the power consumption by more than 50% relative to a conventional type of relay apparatus. Furthermore all of the magnetic flux is concentrated in a magnet circuit passing through the single electromagnetic coil, so that it is necessary for the cross-sectional area of the central aperture of that electromagnetic coil (i.e., an aperture into which the corresponding plunger is drawn) to be large. Hence, the external dimensions of the electromagnetic coil must correspondingly be large, thereby increasing the overall size of the relay apparatus. In addition, the manufacturing cost will be high, due to the large amount of copper which must be used to form the single electromagnetic coil.
Furthermore, there will be differences between the forces applied by the respective plungers of the two solenoids when activated), on the corresponding contact switches, so that the characteristics of the two relays will be unbalanced.